Why ask a human being who might have the exact knowledge you are looking for when you can ask the "dumb machine of making things up and getting things wrong" instead.
Now being serious, LLMs are nondeterministic loosy compression algorithm which return "what a plausible answer to that question would be". They have no world model, no truth verification and formally will be excellent while having no verifiable content.
Yeah, but despite that they work pretty good lately if what you're asking is verifiable, like searching for the name of a book.